Don't we need a comma before in which?
Technically, the usage of a comma before which depends on whether the noun modifier is ESSENTIAL or NON-ESSENTIAL
* If the noun modifier is essential
, ==> NO comma
before "which" or "that"
* If the noun modifier is non-essential
==> Have a comma
* No comma before "that"
Regarding this question, you cannot put a comma before "in which", [not before "which"], because if you put a comma, the relative clause will be a non-essential clause and can be eliminated. However, if the relative clause "in which the floor....." is eliminated ==> the sentence makes no sense.
Hope it helps.
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